Adjustment of muscle length during tendon transfer procedures and tendon repairs is a necessary element in obtaining maximum force from the transferred muscle. A muscle that is set at a length different than the optimal muscle length will not be able to develop maximum force. Usually, surgeons rely on their own experience in determining the amount of tension for setting a muscle to its optimal muscle length, and it is not uncommon for the surgeon to overpull the muscle during the tendon transfer.
Adjustment of muscle length during tendon transfers has always presented a problem for the hand surgeon, because the force developed by an activated muscle is length-dependent. The objective of the surgeon in any muscle transfer should be to restore the transferred muscle to its optimal length. Previously guidelines for adjusting muscle length generally were based on total muscle excursion and the passive tension felt during surgery. The passive tension felt during surgery depends not only on the length of the muscle and inherent qualities of the individual muscle fibers, but also on the surrounding connective tissue adhesions.
While passive tension is important for the assumption of functional position, it is a poor predictor of muscle function. If the muscle is paralyzed or under tourniquet control, extrinsic factors are eliminated, and the muscle exerts passive tension but not active tension. Thus, methods for tendon transfer that depend on passive tension give no information on how the muscle will later function in the patient. Moreover, there are no accurate pratical clinical or physiologic guidelines for assuring that optimal muscle length is restored following tendon transfer procedures.
Over the years, much work has been done on the problem of restoring a muscle to its optimal muscle length during tendon transfer procedures. For example, in the publication of Omer et al, entitled "Determination of Physiologic Length of a Reconstructed Muscle-Tendon Unit Through Muscle Stimulation", published in the Journal of Bone Joint Surgery, Vol. 47, 1965, the determination was made that each muscle has an optimal length at which force is maximal, and the authors developed a procedure involving electrical stimulation of the muscle during surgery to estimate "ideal muscle resting tension". This method was improved upon over the years, but the procedure is still time consuming and complicated, and has not found wide surgical acceptance.
Furthermore, attempts have been made to set the sarcomere length (the portion of the striated muscle fibril lying between two adjacent Z dark lines, otherwise know as Krause's membranes) to a value that is close to the peak of the length-activated tension relation (adjusting the length of the muscle so that the active tension is at maximum with the body portion, e.g. wrist or hand, in the position of function). These attempts must include some accurate means for measuring the sarcomere length.
For example, the publication to Sandow, entitled "Diffraction Patterns of the Frog Sartorius and Sarcome Behavior Under Stretch", published in the Journal of Cell Compar. Physiol., Vol. 9, 1937, mentions employing an optical system for diffracting light through frog sartorius tissue and photographing the grating patterns of the regular alternation of transverse dark and light bands of the component muscle fibers. It was determined that a muscle may be a set of "superimposed gratings", as if the muscle were a singe grating whose grating element distance is the length of the sarcomere of the muscle (the length S of the sarcomeres in the diffracting segment can be determined by means of the grating equation: n.lambda.=S SIN.theta..sub.n, where n is the order of the spectrum; .lambda., the wave length of the light employed; and .theta..sub.n the angle of diffraction of the n.sup.th order spectrum). However, the Sandow apparatus used to determine sacromere characteristics by light diffraction does not utilize a laser or the like, is cumbersome, difficult to support tissue under examination, and lacks practicality.
The patent literature contains some examples of fiber measurement. Thus, the device of Troll et al (U.S. Pat. No. 3,659,950) measures fiber width rather than an axial spacing. The device of Hansler (U.S. Pat. No. 3,804,529) measures axial spacings that are large compared to a laser beam diameter and thus requires that the fiber be continuously moved relative to the laser beam to obtain a measurement. Patents which show laser measuring devices of various types include U.S. Pat. Nos. 3,518,007, Ito; 3,698,817, Iimura et al; 3,858,981, Jaerisch et al; 3,664,739 Pryor; and 4,483,618, Hamar.
No method or apparatus for its practice has previously been available which incorporates the use of laser diffraction for the accurate determination of muscle sarcomere length IN VIVO, nor has there been a successful procedure for accurately restoring tendons during surgical transfers. Moreover, there is a great need for such an apparatus and method which will enable a surgeon to repair and restore muscles so that the muscles may have the ability to function at a maximum force in an awake patient.